—Why does the lake smell terrible?
—Because large quantities of water .
A. have polluted.
B. is being polluted.
C. has been polluted.
D. have been polluted.
网友回答
A. have polluted.
B. is being polluted.
C. has been polluted.
(答案→)D. have been polluted.
解析：从问句和答语可知说的是湖的现在的情况，又因为强调污染对湖所产生了一定的结果和影响，故在C，D中选择正确答案。由于主语是quantities，谓语动词要用复数。故选D。